An anal fistula, otherwise known as an anorectal fistula, is an abnormal passage formed between the wall of the anal canal and the skin around the anus, typically the perianal skin. An anal fistula usually originates from an infection in an anal gland located in the anal canal. In the case of an anal gland becoming infected, an abscess may form deep under the skin around the anus which requires surgical drainage. After drainage, a tract between the drainage site and the wall of the anal canal may form resulting in an anal fistula. Fistulas cause intermittent symptoms of discharge and generally do not heal without treatment or surgical intervention. Anal fistulas are also a common feature of inflammatory bowel diseases, especially ulcerative colitis and Crohn's disease.
‘Lay open’ fistulotomy is the conventional surgery for treating an anal fistula and involves dividing the tissue between the fistula and the skin so as to promote tissue regeneration and hence healing of the fistula. A disadvantage with this procedure is that it causes discomfort and scarring, and usually results in some level of incontinence.
In an alternative procedure, a seton may be used which is passed through the track of the fistula by use of a fistula probe. The seton is a string preferably formed out of silicon or rubber that is typically threaded through an eye of the fistula probe. The probe is then passed through the track of the fistula pulling the seton along so that it extends through the entire length of the fistula. As the probe reaches the wall of the anal canal, the probe is passed through the anus and then removed from the seton such that the two loose ends of the seton can be tied together so as to form a loop. The seton is typically either left in place long-term and assists in draining any discharge from the fistula, or is tied tight to produce a slow form of fistulotomy, that is, division of tissues superficial to the fistula.
Suitable devices for use in such a procedure are described in the prior art. For example, patent application WO 2005/020823 describes a device for the treatment of anal fistulas comprising a probe attached to a drainage thread. The probe is used to guide the drainage thread through the fistula, after which the probe may be removed and the two ends of the thread tied together. The thread acts to ensure that the fistula channel is kept open, allowing adequate drainage.
In some cases, particularly Crohn's disease, when the fistula becomes infected, it may be necessary for the patient to undergo a course of antibiotics and/or anti inflammatory medication prior to surgical treatment. Consequently, surgical treatment of the fistula is delayed causing discomfort. In an attempt to overcome this problem, Razvan Arsenescu has proposed the development of a biodegradable seton made from PLGA that releases an anti-inflammatory drug in a controlled fashion (see the proposal for an award from the Kentucky Science & Engineering Foundation entitled “Drug Eluting Biodegradable Seton for Treatment of Perianal Fistulas in Crohn's Disease” at http://ksef.kstc.com/Dynamic/Awards).
A problem with the conventional technique is that the knot of the seton is external to the body and may cause discomfort as the patient sits down. In some cases the knot becomes undone causing the seton to fall out of the fistula and so the process of inserting the seton needs to be repeated.
A further problem is that whilst movement of the seton within the fistula is desirable to assist in drainage, such movement may act to prevent tissue regeneration and hence healing of the fistula. Further surgical steps to close the fistula are therefore often required after the elimination of the infection.
As already indicated, an alternative to the above procedure is that the seton can be used to gradually divide the tissue superficial to the fistula. In this alternative procedure, the structures superficial to the fistula, such as the skin, subcutaneous fat and sphincter muscle, are slowly divided by tying the seton tightly. The process of gradual tightening causes the seton to divide the tissue it surrounds thereby promoting tissue regeneration and healing of the fistula. Unfortunately, this often results in some impairment of continence.
A device suitable for use in such a procedure is described in patent application WO 2005/096957. The device describes a silicone thread with either a transversal through hole at its tip or a tip-piece that includes a transversal through hole. Also provided is a removable supporting jacket which serves to guide the thread through the fistula. Once the thread has been passed through the fistula, the supporting jacket is removed and the distal end of the thread is passed through the transversal through hole at the tip. Fastening nodes may be provided along the length of the thread so as to interfere with the internal diameter of the transversal through hole, thus tying the thread. When tied tightly, a slow cutting action is provided resulting in the opening-up, or “elastic traction” of the fistula. In use, as the loop slackens due to the cutting action, more of the thread along with further fastening nodes may be pulled through the transversal through hole so as to ensure that the cutting action is maintained.
The main disadvantage of dividing the tissue in this way is that it tends to result in some level of incontinence. Furthermore, the lose ends of the thread may again cause discomfort as a patient sits down, and rotation of the tightened thread through the fistula may cause additional discomfort and risk of infection.
As fistulas vary in configuration, complexity and length, surgeons have to take great care when inserting a probe and seton through the track of a fistula as surrounding tissue can easily be damaged as a result of the probe going off course. Furthermore, a seton is typically attached to the probe by the seton being inserted through an eye of the probe, or by an end of the seton overlapping an end of the probe and the ends being lashed together using a thread. These types of connections are bulky and may cause the seton to abrade or damage surrounding tissue as the seton is pulled through the fistula. Furthermore, it is also apparent that these configurations are often inadequate at maintaining the seton attached to the probe because the seton may become detached from the probe as it is pulled through the fistula. In such cases, the surgeon would need to repeat the procedure which potentially causes more trauma to the surrounding tissue and the patient.
In an attempt to avoid fistulotomy (the division of tissues superficial to the fistula track), an alternative recent procedure using a fibrin plug has been introduced. The fibrin plug comprises a scaffold of polymeric fibrin that is inserted into the fistula tract so as to promote tissue in-growth into the scaffold so as to restore natural tissue healing and formation.
A disadvantage with the fibrin plug and even its more recent modifications is that it tends to fall out of the fistula before the end of the 4 to 6 week healing process. Although the fibrin plug can be sutured to an inner wall of the anus to mitigate against this problem, this has proven to be insufficient to maintain the plug in position.
In an attempt to overcome the above disadvantages, a modified fibrin plug is disclosed in US patent application US 2007/0031508. The modified fibrin plug includes end caps and/or a “tail” which may be sutured to the patient after placement of the plug so as to secure the plug in position. Such a device again relies entirely on the strength of the sutures and surrounding tissue. Thus, whilst this represents an improvement on the conventional fibrin plug, it does not reliably overcome the problem of plug displacement.
There is also a need for devices that will enable other types of fistulas to be treated.
Such fistulas include for instance recto-vaginal fistulas, which are abnormal passages between the rectum and the vagina. These are particularly difficult to treat by conventional surgery. Recto-vaginal fistulas frequently recur requiring multiple operations resulting in bowel incontinence, pain and deformity. Recto-vaginal fistulas have become a bigger problem of late due to a rising incidence of inflammatory bowel disease (especially Crohn's disease), as well as operations to preserve continence for ulcerative colitis sufferers, by restorative proctocolectomy and ileal pouch anal anastomosis. Such procedures are also being performed on patients suffering from a variety of premalignant conditions. There is therefore a need for devices and procedures which will give a high chance of achieving primary healing in recto-vaginal fistulas without invasive surgical intervention.
The present invention seeks to provide a device that overcomes or substantially alleviates the problems mentioned above.